Substantial evidence has been obtained which supports the concept that insulin-like growth factor I (IGF-I) is an autocrine/paracrine regulator of ovary function. Under physiological conditions, IGF-I is bound with high affinity to a family of binding proteins (the IGFBPs) which act to modulate, either amplify or attenuate, IGF-I action. Recently we have isolated, sequenced, and cloned the six rat IGFBPs (IGFBP -1,-2,-3,-4,-5,-6), and obtained preliminary evidence from Northern analysis that the messenger RNA transcripts for the IGFBPs are expressed in the rat ovary. To understand IGF-I function from a physiological perspective, we must understand the cellular localization and regulation of these six IGFBPs in ovary. This is the overall objective of this grant application. In the first aim, we will employ in situ hybridization to localize the cellular sites of the mRNAs for the six IGFBPs in rat ovary tissue throughout the estrous cycle. Interestingly, preliminary data suggest that each of the IGFBPs may be localized to a different population of endocrine cells. In the second specific aim, we will synthesize fragments of each of the IGFBPs and use them as antigens to elicit the production of antibodies. Then by immunocytochemistry we will characterize the cellular localization of the six IGFBPs in ovary tissue during the estrous cycle. In the last specific aim we will perform a series of classic endocrine ablation and replacement experiments to obtain basic information about the hormonal regulation of IGFBP production. Changes in the expression of the six IGFBPs will be monitored by in situ hybridization and immunocytochemistry. We expect that the results of these specific aims will provide primary answers to the "next step" questions in the field of IGFBPs in the ovary, and provide the rational for future studies of the regulation and function of the ovarian IGFBP system.